1. Field of the Invention
This invention relates to printers, and more particularly to printers having a mechanism for detecting a paper-out condition and a column one position.
2. Description of the Prior Art
In the past, paper-out detection has been done using a limit switch. These switches are very sensitive to changes in paper thickness and are difficult to adjust.
Optical devices have also been used to detect a paper-out condition. These optical devices ordinarily are equipped with a light emitting diode (LED) to shine on the paper and a photo transistor to receive the light reflected from the paper. These optical devices are very sensitive to ambient light levels and therefore must be shielded from any outside light source, but still must be open to the extent that the light is permitted to shine on the paper and reflect back. They are also susceptible to debris dropping from the paper or from the printer mechanism, which debris may obscure the light path.
In the prior art, end position of the carriage has been detected by simple electromechanical switches which are very sensitive and difficult to adjust. They also tend to be rather short lived. Optical reflection devices as mentioned above have also been used for detecting the end position of the carriage. Also, a pad associated with the carriage or the head has been used to interrupt a light beam between an LED and a photo transistor.
In the present invention, a lever attached to the carriage contacts the detection lever arm, moving it from its normal state and causing the LED to transmit light to the photo transistor.
There is no known mechanism in the prior art which employs essentially the same components for both the paper-out condition and column zero position detection. This invention also eliminates the sensitivity to debris, adjustment and paper thickness, transferring a gross mechanical movement to a very precise optical beam. Ambient light has no appreciable effect on this optical sensor.